NEW YORK (AP) — Wal-Mart Stores Inc. is expanding a test of a new checkout program that allows shoppers to scan items with their smartphones while they're in the aisles and then pay at self-checkout terminals.

The world's largest retailer launched what it calls its "Scan & Go" program late last year in about 70 stores in Atlanta and in the Bentonville, Ark., area, where the retailer is based. It is now testing the program in more than 200 stores in markets including Dallas, Houston, Austin, Texas; Denver, Portland, Ore., Seattle, and Phoenix.

The pilot program will still be in a small number of Wal-Mart's more than 4,000 stores in the U.S. But it's part of the company's overall strategy to involve customers' increasing use of smartphones.

More than half of Wal-Mart's customers have smartphones, and 40 percent of traffic from walmart.com is coming from shoppers' mobile devices, said Gibu Thomas, senior vice president of mobile and digital initiatives at Wal-Mart's global e-commerce division.

"Our goal is to give choices to all of our customers however they want to shop," Thomas said during an interview with The Associated Press Wednesday. "It's part of a holistic program to empower the customer."

The program works like this: Customers scan bar codes of the different products using the retailer's Scan & Go app downloaded onto Apple Inc. iPads, iPhones or iPod Touch devices. The app generates a code, which can be scanned at the self-checkout terminals.

The app is only available for Apple devices but Wal-Mart says it has plans to eventually release versions for other platforms.

Wal-Mart, meanwhile, has been expanding its self-checkout terminals and plans to add more than 10,000 self-checkout registers by the end of this year in the U.S.

The pilot program has been well-received so far by customers, with more than half of the shoppers who tried the "Scan & Go" app using again, Thomas said. He noted it's a good way for shoppers looking to keep a running tally of how much they're spending as they place the products in their carts — instead of being surprised at the cash register.

But Thomas also noted that the new service has also appealed to shoppers who like to do their own bagging of groceries. Shoppers can pick up bags at the front of the store and organize the groceries in the bags the way they want.

"They like to bag items the way they keep their items in the house," he said.